There may be difficulties obtaining clear television pictures with television sets and antennas situated interior to dwellings. The signals penetrating houses and apartments are attenuated and reflected causing the reception to be weak and producing multiple reflected signals due to reflections from within and outside of the building. These reflected signals arriving from different directions and different paths result in undesirable ghosts or multiple pictures in the video reproduction. In this indoor signal environment the television set owner typically uses “rabbit ears,” an antenna including variable length swiveled or pivoted dipole/loop elements located on top or near the television receiver (e.g. as disclosed in U.S. Pat. No. 3,478,361). The operator adjusts the length and orientation of dipole elements to increase the signal strength and reduce the multiple reflection causing visible multiple pictures or ghosts on the television screen.
While the above discussed problems regarding ghosts and multiple pictures may be associated with the National Television System Committee (NTSC) standard for analog television transmission, the transition to the Advanced Television System Committee (ATSC) standard that defines digital TV (DTV) transmission is already underway. The effect of multi-path (reflections) on digital signals is more severe. It is a characteristic of digital transmissions that they are generally received perfectly or not at all with the transition region in signal strength being very sharp. Thus, in a marginal reception area such as indoors, a slight increase in signal strength due to the gain of the antenna or the rejection of a reflected signal due to the directivity may result in the difference between receiving a signal and not receiving it at all.
Although other indoor television antennas exist using configurations of loops, dipoles, wires, and electrical circuits, these existing antennas are deficient in directivity and gain needed to receive desired direct signals and to discriminate against reflected and depolarized signals. Impedance matching is often circuits which are non-compensating with frequency change. Existing indoor antennas may not have accurate and repeatable mechanisms for repositioning and tuning on different channels. Further disadvantages of existing indoor TV antennas include the complexity of matching circuits, some of which need electrical power and the large physical dimensions of dipoles and loops.
Conventional VHF/UHF television broadcast receiving antennas are typically designed to receive signals from only one direction. They are often referred as “unidirectional antennas.” This unidirectional feature rejects undesirable multipath signals, which may cause multipath or “ghost” interference problems.
Circularly polarized waves can have a useful property of reversing sense upon being reflected. For instance, a right hand circularly polarized (RHCP) wave bouncing off a metal building becomes left hand circularly polarized (LHCP). Television systems transmitting and receiving with circularly polarized (CP) antennas can reject many reflected signals due to their crossed senses of rotation, reducing ghosting in analog TV or aliasing in digital TV.
Frequency reuse and channel diversity increasingly require antennas with multiple look angles and broad instantaneous bandwidths. Television broadcasting may someday benefit from cellular like infrastructures, in which programming is received simultaneously from multiple directions and frequencies.
Various antennas and/or reflectors, such as broadband antennas and spiral antennas, are disclosed in U.S. Pat. Nos. 2,863,145, 2,969,542, 3,131,394, 3,144,648, 3,299,355, 4,085,406, 4,095,230, 4,143,380, 4,503,101, 4,608,572, 5,990,835, and 6,424,317.
However, there is a need for a relatively inexpensive indoor home TV antenna that is circularly polarized, is able to receive multiple simultaneous beams, and includes instantaneous broadband spatial response, i.e. may output all VHF/UHF channels by all azimuthal beams simultaneously.